1. Field of the Invention
This invention relates generally to postage scales adapted to weigh an article and determine the appropriate postage to be applied thereto. More particularly, the present invention is directed to an interface which enables a postage scale processor to communicate with a plurality of peripheral devices associated with a mailing system.
2. Related Applications
The present invention includes an interface board which interconnects a postage value determining system processor with a plurality of peripheral devices associated with a mailing system. In a copending application of Daniel F. Dlugos entitled Multiprocessor Parcel Postage Metering System Having Serial Data Bus, Ser. No. 13,734, filed Feb. 21st, 1979 and assigned to the assignee of the preesent invention, now issued as U.S. Pat. No. 4,308,579 a postage calculating system having a serial communications controller for communications between the system processor and peripheral devices was disclosed. The system included a serial communications but through which the peripheral devices communicated with the system processor. Some peripherals were interconnected to the serial communications bus by a separate peripheral controller, while a meter setting device was directly linked to the serial communications bus. Appropriate signals were transmitted along an attention line when it was desired to select a peripheral which would receive or transmit via the shared communications bus. Acknowledgement lines were also provided to acknowledge receipt of signals. The serial communications controller comprised an integral part of the main postage calculator system circuit board.
Since the serial controller was an integral part of the main scale system circuit board, a purchaser who only wished to acquire a postage scale and not the peripheral devices or not all of the available peripherals was at a disadvantage. In addition, if a malfunction arose, the serial communications controller and the communications bus were not serviceable as a single unit on a separate board.
The sharing of a common communications bus by all peripheral devices made the replacement or substitution of different peripheral devices a formidable task which required reprogramming.
A serial communications system between a postage meter control unit and a plurality of external devices has been disclosed in copending application of John H. Soderberg et al entitled Electronic Postage Meter Having Plural Computing Systems, Ser. No. 89,413, filed Oct. 30, 1979, and assigned to the assignee of the present invention now issued as U.S. Pat. No. 4,301,507. The communications protocol procedure disclosed in such application related to the serial transmission of data and bit by bit return of such data to the transmitter verification. This copending application disclosed a system comprising a daisy chain between a plurality of external devices and a control unit. It should be appreciated that a communications buffer comprised of a daisy chain prolonged the time required for the transmission of data especially when one considers the bit by bit return for verification of transmitted data. Further, the possibility that a device along the daisy chain might introduce error was present.